It is desirable in the processing of tobacco to produce a product having a moisture content within certain limits. The limits become particularly critical in the case of tobacco shipped abroad and subject to import taxation. The tobacco is contained in shipping containers and is presumed by the taxing authorities to have a specified moisture content. Should the moisture content be higher than that stated, the excess water is taxed as tobacco resulting in an unnecessary tax expense. The extra water also incurs undue shipping costs.
Thus, the tobacco industry traditionally, at least in the case of tobacco for export to certain countries, has resorted to considerable expense to produce the tobacco within closely controlled moisture content limits. This is accomplished by drying the tobacco to a high degree of dryness, cooling it and then remoistening it with steam. By way of example, for tobacco to be shipped abroad, the tobacco may be dried to as little as 6-7% moisture in order to obtain a final moisture content of about 11%.
Following the drying and remoistening steps, the tobacco is moved on a series of conveyors, one being a climbing conveyor, to the top of a packing tower where the tobacco is introduced onto a cross-conveyor which is capable of being reversed in direction to feed the tobacco into one of a pair of charging tubes. From each tube the tobacco flows into a shipping container. A hydraulic plunger is associated with each charging tube to press the tobacco into the shipping container, after which the container is capped. After filling of one of the shipping containers is completed, the cross-conveyor is reversed in direction to fill the other container.
Traditionally, the moisture content of the tobacco charged to a shipping container is measured by a moisture determining means positioned at the outlet end of the drying and remoistening apparatus. This permits the operator of the drying and remoistening apparatus to determine the moisture content of the tobacco as it comes out of the apparatus and to immediately make any corrections or adjustments in the apparatus that are necessary in order to obtain, as close as possible, the desired moisture content. While this does permit quick adjustment of the drying and remoistening apparatus, it is apparent that the moisture content in any particular shipping container can vary from that desired primarily due to drying of the tobacco between the moisture determining apparatus and the charging tubes. Thus, in order to obtain a moisture content of 11% in a particular shipping container, the tobacco may have to be remoistened to as much as 11-1/2%. The problem is that the rate of drying will vary dependent upon ambient temperature and humidity conditions, and an operator may unwittingly introduce into a shipping container tobacco having a moisture content above the desired 11%. In addition to resulting in excess taxes and shipping costs, too high a moisture content can cause spontaneous combustion of the tobacco and destruction of at least part of a shipment.
As a further problem, the tobacco industry traditionally has employed moisture readers which take a moisture reading only of samples of the tobacco being processed. The assumption then has to be made that the readings obtained are average readings representative of the entire product flow. Clearly, substantial variations can occur in the moisture content of the product limiting the usefulness of the sampling technique.